Devices which have selenium as constituent parts thereof



April 18, 1950 D. W. RAU El AL DEVICES WHICH HAVE SELENIUH AS CONSTITUENT PARTS THEREOF 1 Filed July 28, 1948 fvl zzvroas Dav/0 h/ Rnu and BY Huausr H. BRUEMI'I R Patentcd Apr. 18, 1950 DEVICES WHICH HAVE SELENIUM AS V CONSTITUENT PARTS THEREOF David W. Rau, Kirkwood, and August H. Bruemmer, St. Louis, Mo., assignors to Vickers, In-

corporated, a corporatio n oi Michigan Application July 28, 1948, Serial No. 41,044

9 Claims.

This invention relates to improvements in devices which have selenium as constituent parts thereof. More particularly this invention relates to an improved method of making devices which have selenium as constituent parts thereof.

It is therefore an object of the present invention to provide an improved method of making devices which have selenium as constituent parts thereof.

In the manufacture of devices which have selenium as constituent parts thereof, it is customary to place selenium in intimate and adheringcontact with a base plate, and then cover the selenium with an overlying metallic electrode or lighttransmitting electrode. In the first instance the resultant product is an electrical rectifier, and in the second instance the resultant product is a photo-electric cell. In both instances the selenium coating tends to coact with the overlying electrode to provide certain desired electrical characteristics.

Where the devices which have selenium as constituent parts thereof are to be used to rectify alternating current, it is desirable that the selenium offer strong resistance to current flow in one direction while offering but. little resistance to current flow in the other direction. Selenium inherently provides a greater resistance to current flow in one direction than the other, but it is desirable to further increase the resistance to current flow in the one direction. methods have been proposed and used for effecting increased resistance to current flow in the one direction while maintaining low resistance to current flow in the other direction; and some of those methods have been useful. However, while use ful, many of the methods are useful on a laboratory scale only and are not useful on a commercial scale. For example, the methods which include bringing the fumes of ammonium chloride, or sulfur, or potassium thiocyanate, or concentrated sulfuric acid into contact with the selenium may be quite usable in a laboratory staffed with highly skilled personnel, but they are far too risky for use in commercial establishments employing semi-skilled personnel. Other methods, which are less risky are nevertheless not suited to large scale production because of the cost involved in carrying them out. For example, methods which require the washing or immersing of the selenium, to enhance the electrical characteristics thereof, are objectionable because they introduce the problem of drying the devices and of handling quantities of solutions. This not only requires time, but the time will vary as the ambient humidity varies. Still other processes are Various objectionable because they rely upon inefficient or unduly'expensive reagents to attain the desired results; and they may also require exceedingly close control of the concentrations involved. In addition, some methods require washing of the selenium after treatment, and still other methods require individual handling which cannot be given readily on production lines. For these various reasons prior methods of treating selenium, to enhance its ability to oifer considerable resistance to current flow in one direction while minimizing resistance to current flow in the other direction, are objectionable. The present invention obviates these objections; and it is therefore an object of the present invention to provide a new and more useful method of enhancing the ability of selenium to resist current flow in one direction while minimizing resistance to current flow in the other direction.

The method of the present invention conducts nascent ozone into direct contact with the selenium, and it uses that ozone to enhance the ability of the selenium to resist current flow in one direction; and the ozone does this without materially increasing the seleniums resistance to current flow in the other direction. The use of the v ozone is highly desirable because it is not harmful to personnel, it does not require washing of the selenium after treatment, it is inexpensive, it is a gas and thus avoids the problem' of drying the selenium, and its concentration does not have to be closely controlled. It is therefore an object of the present invention to conduct nascent ozone into direct contact with the selenium surface of articles which have selenium as constituent parts thereof.

Other and further objects and advantages of the present invention should become apparent from an examination of the drawing and accompanying description.

In the drawing and accompanying description a preferred embodiment of the present invention is shown and described but it is to be understood that the drawing and accompanying description are for the purposes of illustration only and do not limit the invention and that the invention will be defined by the appended claims.

In the drawing Fig. 1 is an end elevational view of a chamber and an ozone generator usable in the process provided by the present invention, and

Fig. 2 is a partially sectioned, side elevational view of the chamber and ozone generator of Fig. 1.

Referring to the drawing in detail, the numeral l0 denotes a chamber which is used to receive desupport a number of devices which have selenium as constituent parts thereof. These devices are denoted by the numeral I8; and they will usually take the form of base plates which have a, selenium coating adherent to the upper surfaces thereof. A cover 28 is provided for the chamber I8. With the exception of adit I2 and exit I4, the chamber is substantially air-tight and will exclude extraneous gases while confining the ozone.

The cover 28 of the chamber I8 has an opening in the top thereof; and a depending nozzle 22 of a vertically disposed tube 24 extends down through that opening in the cover 28. The vertically disposed tube 24 is preferably made of glass, and it has a side arm inlet 26 at the upper end thereof. With this tube, air or other gases can be introduced into the side arm inlet 26 for passage downwardly through the body of tube 24 and out of the nozzle 22. The lower end of the nozzle 22 extends below the top of the cover 28 of chamber I8; and it is directed downwardly toward the base plates I8 on the platen I6. As aresult, any gases issuing from the nozzle 22 are directed downwardly into contact with the base plates I8 and the selenium coatings thereon.

A vertically disposed tube 28 is positioned concentrically within the vertically disposed tube 24; and it has a diameter appreciably smaller than the diameter of the tube 24. Consequently there is an annular passage for air or other gas between the exterior surface of tube 28 and the interior surface of tube 24. An elongated electrode 38 is positioned concentrically within the inner tube 28, and that electrode projects outwardly from the top of the tube 28. A sodium chloride solution 32, or other electrolyte, is confined and held within .the inner tube 28, which tube also is preferably of glass. The sodium chloride 32 constitutes an electrode in intimate contact with the entire lower surface area of the inner, vertically disposed tube 28; and it conducts the charge from the electrode 38 to the inner surface of the tube 28. A stopper 34 is disposed in the openings at the open upper ends of the tubes 24 and 28; and it serves to close those upper ends. The stopper 34 has a minute opening therethrough to receive the electrode 38, and the stopper 34 holds the electrode in position relative to the tube 28.

The upper end of the electrode 38 is connected to one end of the secondary winding 36 of a high voltage transformer. The other end of the secondary winding 38 of the high voltage transformer is connected to an annular electrode 38 that'is mounted on an elongated sleeve electrode 39. The electrode 38 conducts the charge from the other end of the secondary winding 38 to the sleeve electrode 39, and the sleeve electrode 39 is in intimate contact with the exterior of the outer vertically disposed tube 24. Thus, the annular space between the inner surface of outer tube 24 and the outer surface of inner tube 28 is disposed between the cylindrical, liquid electrode ,32 and the sleeve electrode 39; and air or other gas in that annular space is subject to any silent corona discharge created by electrodes 32 and 39.

The primary winding 48 of the transformer is preferably connected to a. suitable source of alternating current; as for example, an outlet in a factory or other industrial establishment. The number of turns on the primary and secondary windings 48 and 36 of the transformer is so calculated as to raise the potential between the ends of the secondary winding 36 to a value at which a silent corona discharge occurs in the annular space between the inner surface of tube 24 and the outer surface of tube 28. This discharge will generate ozone when either oxygen or air is passed through that space; and that ozone will be directed downwardly from the nozzle 22 and onto the base plates I8 on platen I6. Spent ozone and air will ordinarily issue from the chamber I8 through adit I2 and exit I4; but where it is desired to use doors for adit I2- and exit I4, an exhaust outlet 42 can be provided in the cover 28 of the chamber I8 so that air and spent ozone can exhaust from the chamber I8.

The process of the present invention contemplates the formation of a layer or coating of selenium upon a suitable base plate I8, the conversion of that layer or coating to the grey crystalline form of selenium, and then the bringing of a quantity of nascent ozone into engagement with the selenium layer or coating. The layer or coating of selenium can be made in several different ways; one method contemplating the heating of the base plate and the rubbing of a stick of selenium against the heated base plate until the selenium melts, runs onto and adheres to the base plate. Another method contemplates distributing selenium powder over the surface of a heated base plate until the base plate melts the powder and causes it to adhere to the base plate. Still another method of forming the selenium layer on the base plate contemplates evaporating selenium onto the base plate. The most preferred method contemplates the sprinkling of selenium powder onto a heated base plate to form an initial selenium layer, sprinkling a second layer of selenium powder onto the base plate, and then placing the twice sprinkled base plate in a heated press where the two layers of selenium are made to adhere to each other and to the base plate. In each of the methods, the selenium coated base plate is heat treated to convert the selenium layer or coating from the amorphous to the grey crystalline state.

No matter how formed, the selenium coatings on the base plates I8 should be in, the grey crystalline state; and in this state the coatings need only an accentuation of their natural electric characteristics. As the base plates I8 are introduced into the chamber I8, as by being placed upon platen I6, air or oxygen is introduced into the outer tube 24 through side arm opening 26. The air or oxygenwill pass downwardly throughin one direction'while not materially increasing resistance to current flow in the other direction.

Where oxygen is introduced through the side arm inlet 26, the concentration of ozone generated in tube 24 is preferably between zero and fourteen percent; and usually it will be about-sevenpercent. Where air is introduced through the side a'rm inlet 26, the concentration of ozone generated in tube 24 will preferably be between zero and two percent; and usually it will be about one percent. The time the base plates It! should remain in the chamber In is not highly critical; the greater the percentage of ozone the shorter the time the base plates l8 need be treated. Where the concentration of ozone is about one percent, the time of treatment can be as short as one half minute or as long as ten minutes.

In one embodiment of the present invention, the outer tube 24 has an outside diameter of one inch, the inner tube has an outside diameter of approximately five-eighths of an inch, and the transformer winding 36 provides a potential of twelve thousand volts. With such an arrange ment, air can be passed through the annular space between the inner tube 28 and the outer tube 24 to generate nascent ozone; and that ozone will materially improve the electrical characteristics of selenium where that selenium is treated for three minutes. However, neither the size of the tubes 28 and 24 nor the potential of the transformer, nor the time of exposure is highly critical. Variations, within limits, may be made in each of the factors involved in the method without adversely affecting that method.

The results obtained by use of the method provided by the present invention are very satisfactory, and they evidence a considerable enhancement of the ability of the selenium to resist current flow in one direction without materially increasing resistance to current flow in the other direction. For example, one plate from a set of selenium coated base plates, which when provided with metallic counter electrodes experienced a forward voltage drop of ninety eight one hundredths volts and an inverse voltage drop of fifteen and two tenths volts, had a forward voltage drop of ninety four one hundredths volts and an inverse voltage drop of twenty one and four tenths volts where the selenium coating had been treated with nascent ozone for one half a minute. Another plate from the same set of plates was treated with nascent ozone for a full minute; and it then had a forward voltage drop of ninety seven one hundredths volts and an inverse voltage of twenty one and eight tenths volts. Still another base plate from the same set of plates was treated with nascent ozone for three minutes, and it had a forward voltage drop of ninety six one hundredths volts and an inverse voltage drop of twenty three volts. When another plate, from the same set of plates, was exposed to nascent ozone for five minutes, that plate had a forward voltage drop of ninety two one hundredths volts and an inverse drop of twenty two and two tenths from one half minute to ten minutes duration.

volts. Another plate, from the same set ofplates, was exposed to nascent ozone for ten minutes and had a forward voltage drop of ninety five one hundredths volts and an inverse voltage drop of twenty volts. Exposure of other plates, from the same set of plates, for more than ten minutes to nascent ozone caused those plates to have higher inverse voltage drops than the untreated plates; but the inverse voltage drops of plates receiving prolonged treatment with nascent ozone are less, and the forward voltage drops are greater, than the corresponding voltage drops of plates receiving treatments of Other plates, which when provided with a metallic counter electrode had a forward voltage drop of sixty two one hundredths volts and an inverse voltage drop of twelve and two tenths volts, were treated with nascent ozone for a period of three minutes. Those plates after treatment had forward voltage drops of about seventy six one hundredths volts and inverse voltage drops of about twenty nine and two tenths volts.

With many manufacturers of articles which have selenium as constituent parts thereof, it has become customary to introduce a predetermined amount of halogens into the selenium as inoculants. Such inoculants have been found to be beneficial in some cases, as by increasing the inverse voltage drop of the articles without correspondingly increasing the forward voltage drop of those articles. Where the inoculated plates have been treated in accordance with the principles and teachings of the present invention, it has been found that the effect of the ozone overshadows the effect of the inoculants. Consequently it has been found possible to reduce the amount of inoculant, thus reducing the overall forward resistance of the selenium, and also reducing the cost of the articles by reducing the amount of inoculants required. It is also possible to use inoculants and the ozone treatment together; and proper selection of the inoculants and duration of ozone treatment can produce very desirable electrical characteristics for the selenium coated articles.

In addition to the combined effect obtainable by use of an inoculant in the selenium and the subsequent treatment of the inoculated selenium with ozone, it is possible to use other combinations of ozone treatment with other selenium treatments. For example, in some instances it may be desirable to dip the finished selenium base plate or the semi-finished base plate in a solution, dry it, and then treat the plate with ozone before applying the counter electrode. By proper selection of the clip and by regulation of the duration of the ozone treatment, it is possible to obtain unusually desirable electrical characteristics for the base plates. Under ordinary circumstances, however, the electrical characteristics obtainable with ozone treatment alone are quite adequate; and the extra'cost of the dual treatment is normally not necessary.

The principal difference between the use of oxygen and ordinary air, in producing the ozone required for treatin the selenium, is the concentration of ozone and thus the duration of the treatment. However, since the time of treatment with ozone, obtained from air, can be as short as one half a minute and is ordinarily not over five minutes, the additional cost of using oxygen is not believed to be worthwhile. Particularly, since the extremely desired results described herein were attained with ozone made from air.

The disclosed method of making ozone is not the only method that can be used. Another method which can be used quite readily employs a high potential electrode, with a number of sharp points, disposed above the platen IS on which the articles I8 are supported. Where the platen I6 is a flat metal sheet, a silent corona discharge will occur directly between the multiple points of the overhead electrode and the platen l 6 on which the articles I8 are supported. Under such circumstances the nascent ozone is even closer-to the articles than it is in the device shown in the drawing. The ozone may also be prepared by well known chemical methods; such methods not being preferred because they are more expensive, les easily controlled, and less suited to factory production requirements than are the electrical methods of making ozone.

The platens l8 may be introduced through the adit i2 and may be removed from the exit M by hand; but it is preferred to move the platens l6 through the chamber I0 by a continuously advancing mechanism. Such an arrangement makes it possible to employ this method in production line operations. One continuously advancing mechanism is an endless belt, and another is a reciprocating pusher or puller.

Whereas a preferred embodiment of the present process has been shown and described it should be obvious to those skilled in the art that various changes may be made in the form of the invention without afiecting the scope thereof.

What we claim is:

1. The method of enhancing the ability of selenium to resist current flow in one direction without appreciably increasing its resistance to current flow in the other direction which comprises converting selenium to the grey crystalline form, passing air between spaced electrodes connected to a high voltage source to generate nascent ozone, and directing said ozone onto said selenium for a period of from one half minute to five minutes.

voltage source to generate nascent ozone, and directing said ozone onto said selenium.

4. The method of enhancing the electrical properties of selenium that comprises converting selenium to the grey crystalline form, creating nascent ozone, and directing said ozone onto said selenium.

5. The method 01 enhancing the ability of selenium to resist current flow in one direction without appreciably increasing its resistance to current flow in the other direction that comprises creating nascent ozone and directing said ozone onto said selenium. v

6. The method of enhancing the electrical properties of selenium that comprises passing air between spaced electrodes connected to a high voltage source to generate nascent ozone, and directing said ozone onto said selenium.

7. The method of treating selenium to enhance the electrical properties thereof which comprises creating ozone by a silent corona discharge and directing said ozone onto said selenium.

8. The method of treating selenium that comprises positioning selenium adjacent a silent corona discharge in air.

9. The method of treating selenium that comprises positioning selenium adjacent a silent corona discharge in oxygen so that ozone generated by said discharge can contact said selenium.

DAVID W. RAU. AUGUST H. BRUEMMER.

Name Date Presser Jan. 14, 1930 OTHER REFERENCES Mellor, vol. 10, page 747.

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